Layer silicates probes

The nano-scale structures in polymer layered-silicate nano-composites can be thoroughly characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD is used to identify intercalated structures. XRD allows quantification of changes in layer spacing and the most commonly used to probe the nano-composite structure and... 

Electron spin resonance (ESR) is a useful technique for investigating the mobility and orientation of exchange cations at the surface of layer silicate clays in various states of hydration. Using Cu2+ and the charged nitroxide spin probe, TEMPAMINE+... 

MCBRIDE Paramagnetic Probes of Layer Silicate Surfaces... 

Spectroscopic techniques such as electron spin resonance (ESR) offer the possibility to "probe" the chemical environment of the interlayer regions. With the ESR technique, an appropriate paramagnetic ion or molecule is allowed to penetrate the interlayer, and chemical information is deduced from the ESR spectrum. Transition metal ions, such as Cu2+, and nitroxide radical cations, such as TEMPAMINE (4-amino-2,2,6,6-tetramethylpiperidine N-oxide) have been used as probes in this manner (6-14). Since ESR is a sensitive and non-destructive method, investigations of small quantities of cations on layer silicate clays at various stages... 

Gilman JW, Davis RD, BeUayer S et al. (2005) Use of optical probes and laser scanning con-focal fluorescence microscopy for high-throughput characterization of dispersion in polymer layered silicate nanocomposites. PMSE Prepr 92 168-169... 

The dynamic mechanical thermal analyzer (DMTA) is an important tool for studying the structure-property relationships in polymer nanocomposites. DMTA essentially probes the relaxations in polymers, thereby providing a method to understand the mechanical behavior and the molecular structure of these materials under various conditions of stress and temperature. The dynamics of polymer chain relaxation or molecular mobility of polymer main chains and side chains is one of the factors that determine the viscoelastic properties of polymeric macromolecules. The temperature dependence of molecular mobility is characterized by different transitions in which a certain mode of chain motion occurs. A reduction of the tan 8 peak height, a shift of the peak position to higher temperatures, an extra hump or peak in the tan 8 curve above the glass transition temperature (Tg), and a relatively high value of the storage modulus often are reported in support of the dispersion process of the layered silicate. 

McBride, M. B. (1986). Paramagnetic probes of layer silicate surfaces. In Geochemical Processes at Mineral Surfaces, Davis, J. A, and Hayes, K. F., eds., American Chemical Society Washington, D.C., pp. 362-388. 

U220A14, and layer silicate-rich CS IDP U230A43. (d)-(f) Corresponding X-ray point count analyses obtained from the thin sections on a two-dimensional grid using a 200 keV electron probe with <50 nm spatial resolution at each point. Solid boxed area in (f) shows Mg-Fe-Si composition of the layer silicate and dotted boxed area shows carbonate Mg-Fe composition (source Bradley et aL, 1992). 

Figure 11-2 shows the kinetics of crystallization in the presence of a P40 in an Al-free reaction mixture. To follow the kinetics, crystallization was carried out in a 5 liter-autoclave that could be probed directly. It is seen that crystallization is accelerated with increasing temperature, when compared to syntheses listed in Tables 11-2 to 11-4. Furthermore, this experiment emphasized the metastable character of the new layer silicates. Quartz instead of cristobalite is observed as the final product of the crystallization sequences in the Al-free cases. Crystallization starts at 4 hours and is completed after 9-10 hours. Quartz appears as a product component after 11-12 hours. The growth of quartz ceases after 40-44 hours. From the gradient of the crystallization curve, a growth rate of 15% per hour is determined for this novel silicate under these conditions. 

Atomic force microscopy (AFM) is another technique used to characterize nanocomposites.AFM can provide information about the mechanical properties of a surface at a length scale that is limited only by the dimensions of the AFM tip. AFM tips with 10 nm radius of curvature are readily available from commercial suppliers. When probing mechanical properties, the attractive and repulsive force interactions between the tip and sample are monitored. Schematic depicting the intercalation process between a polymer melt and an organic-modified layered silicate is shown on Figure 6.8. 

X-ray diffraction (XRD), is commonly used to probe the nanocomposite structure. However, XRD can only detect the periodically stacked clay layers, disordered or exfoliated layers are undetected. In general, in layered silicate-filled polymers a coexistence of exfoliated, intercalated and disordered layers is observed. 

In a study of dental silicate cements, Kent, Fletcher Wilson (1970) used electron probe analysis to study the fully set material. Their method of sample preparation varied slightly from the general one described above, in that they embedded their set cement in epoxy resin, polished the surface to flatness, and then coated it with a 2-nm carbon layer to provide electrical conductivity. They analysed the various areas of the cement for calcium, silicon, aluminium and phosphorus, and found that the cement comprised a matrix containing phosphorus, aluminium and calcium, but not silicon. The aluminosilicate glass was assumed to develop into a gel which was relatively depleted in calcium. 

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